Periodontal disease affects a majority of the world's population. The basic cause of the disease is microbial in nature.
It is well-established that hydrogen peroxide and other peroxygen-containing agents are effective in curative and prophylactic treatments with respect to dental plaque, calculus, gingivitis, mouth odor, tooth stains, mucosal infections, and the like.
Most peroxy compounds such as hydrogen peroxide in oral care products tend to be unstable in storage, mainly due to an inherent chemical instability, and also to interaction with other ingredients in the composition. The peroxy compounds decompose within a relatively short period, with a concomitant premature release of active oxygen. Peroxy compounds are difficult to formulate into toothpastes or gels which have an acceptable shelf-life and are capable of liberating active oxygen when applied to an oral cavity.
Many oral care products have been formulated which include a peroxy compound, and more recently oral care products have been developed which include a peroxy compound having improved stability. United States patents which describe peroxy-containing toothpastes, mouthwashes, tablets, chewing gums, and other forms of oral care products include U.S. Pat. Nos. 2,275,979; 3,577,521; 3,657,413; 3,885,028; 3,886,265; 4,226,851; 4,302,441; 4,405,599; 4,426,108; 4,431,631; 4,521,403; 4,522,805; 4,528,180; 4,567,036; 4,592,487; 4,592,488; 4,592,489; 4,687,663; 4,812,308; 4,837,008; 4,839,157; 4,849,213; 4,867,988; 4,891,211; 4,897,258; 4,925,655; 4,971,782; 4,980,152; 4,988,450; 5,000,941; 5,041,280; 5,085,853; 5,256,402; and the like; incorporated by reference.
Both organic and inorganic peroxy compounds have been proposed for use in oral care products, and typically the peroxy compounds exhibit one or more disadvantages which limit their effectiveness in oral hygiene applications.
Sodium perborate and potassium chlorate do not release significant levels of hydrogen peroxide in water. Sodium perborate also is of questionable safety because it contains boron which can undergo systemic absorption.
Sodium percarbonate has a high active oxygen content (15.28% theoretical) and high water solubility. It is produced from low cost starting materials, and it is an environmentally safe chemical. Sodium percarbonate is potentially a superior reagent as a hydrogen peroxide-releasing ingredient in oral care products, except that it is less stable than sodium perborate.
Stabilizers such as magnesium sulfate are suitable for stabilizing sodium perborate, but provide only limited protection with sodium percarbonate. Various methods for stabilization of sodium percarbonate have been proposed.
U.S. Pat. No. 2,380,620 discloses that sodium silicate, magnesium sulphate or gum arabic are unsatisfactory stabilizers when incorporated in sodium percarbonate, but diphenylguanidine lessens the decomposition in the presence of the conventional stabilizers.
U.S. Pat. No. 3,951,838 discloses that prior attempts at chemical stabilization of sodium percarbonate, primarily by magnesium silicate, are generally ineffective in promoting long term stability, particularly in a humid atmosphere. The patent proposes coating of the particles with an aqueous silica sol and drying to accomplish stabilization.
U.S. Pat. No. 4,075,116 describes cocrystallizing of sodium percarbonate with other salts known to form perhydrates such as sodium sulfate, sodium pyrophosphate, sodium glucoheptonate, sodium metaborate, and the like.
U.S. Pat. No. 4,171,28.0 discloses that a non-caking bleach composition may be formed containing up to 6% active oxygen by spraying only sufficient hydrogen peroxide onto sodium carbonate particles to convert a part of the sodium carbonate to sodium percarbonate. U.S. Pat. No. 4,260,408 teaches the addition of sodium phosphate to the composition as a stabilizer. Both patents demonstrate that an assay of less than 6% active oxygen (less than 40% sodium percarbonate) is necessary to obtain satisfactory stability.
There is continuing research and development effort to produce sodium percarbonate in a form which exhibits long term stability under storage conditions, and when incorporated as a peroxygen ingredient in commercial products.
Accordingly, it is an object of this invention to provide sodium percarbonate in a form which is stable under ambient temperature and moisture conditions.
It is a further object of this invention to provide a dentifrice composition which contains stabilized sodium percarbonate, and which releases active oxygen under oral hygiene utilization conditions.
Other objects and advantages of the present invention shall become apparent from the accompanying description and examples.